1. Field of the Invention
The present invention relates to a quantitative determination method for chloride ions in an organism which is applicable to clinical tests.
2. Description of the Prior Art
There is known a quantitative determination method for chloride ions comprising reacting an .alpha.-amylase with a chloride ion-containing sample and a substrate, such as p-nitrophenylmaltoside or starch, by utilizing the phenomenon that an .alpha.-amylase deactivated by a chelating agent is activated by chloride ions Eur. J. Biochem. 41: 171 (1974)!. There is known another quantitative determination method for chloride ions wherein 2-chloro-4-nitrophenyl-.beta.-D-maltoheptaoside is used as a substrate in order to simplify the process for measuring the .alpha.-amylase activity in the above quantitative determination method Clin. Chem., 34: 552 (1988)!.
As a method for measuring the activity of an .alpha.-amylase, there is known a method comprising producing maltose by using an oligosaccharide as a substrate, converting the resultant maltose into glucose and quantitatively determining the glucose obtained to thereby measure the corresponding .alpha.-amylase activity J. Clin. Chem. Clin. Biochem., 17: 705 (1979)!.
Since glucose coexisting in a sample influences a quantitative determination method for a substance in a sample, a method is disclosed in Japanese Unexamined Patent Publication No. 5-76397 wherein glucose in a sample is eliminated by using hexokinase or the like.
Out of the quantitative determination methods for chloride ions, the method using a synthetic substrate such as 2-chloro-4-nitrophenyl-.beta.-D-maltoheptaoside for measuring the activity of an .alpha.-amylase must use the two-point calibration method because linearity in calibration curves is hard to obtain. The known method by using starch as a substrate for an .alpha.-amylase reaction and measuring the reaction product, i.e. a reducing sugar such as glucose and maltose, cannot accurately determine the amount of chloride ions when a blood sample is used, because glucose and maltose are present in blood. Therefore, if a method of newly using a maltooligosaccharide as a useful substrate for an .alpha.-amylase reaction is employed, it will be impossible to achieve an accurate determination because of the interference of glucose and the like present in blood.